Loading state not announced by screen reader

When using the async version of react-select (I'm using v2), the loadingMessage (or other reference to the loading state) is not announced by the screen reader while search results are loading. Instead, the screen reader announces that you have "0 options for search term [x]" until the results load, which is misleading.

This behavior can be seen in the examples on the Async docs page - https://react-select.com/async. I tested using Voiceover on Chrome and Safari, but since the screen reader text is manually provided by react-select (in the A11yText component), this bug should be consistent across screen readers and browsers.

A possible solution is to pass the loadingMessage text to the A11yText component when isLoading is true.

Start with the async select implementation and the A11yText component, then reproduce the behavior from the Async docs example using a screen reader. Trace how loadingMessage and the "0 options" announcement are selected while results load; done means the loading state is announced instead of the misleading zero-options message, with coverage for the loading case.